Apparatus for cutting grooves in a bone

ABSTRACT

A prosthetic device for the human hip having elongated fins or other like protrusions which are provided on the underside of a collar and which extend into previously formed slots or grooves in the bone. Either a plurality of fins, or a single fin having a non-rectilinear shape is provided. Apparatus for formation of the grooves in the bone includes a mill guide which can be mounted onto the proximal end of a rasp embedded in a cavity formed in the bone. A milling bit is used in conjunction with the mill guide to form precisely located and shaped grooves into which the fins can seat. A clamp is provided for securing the prosthetic device to the femur while the cement is hardening.

This application is a division of application Ser. No. 08/183,077 filedJan. 18, 1994, now U.S. Pat. No. 5,480,453, which is a continuation ofapplication Ser. No. 07/979,615 filed Nov. 20, 1992 (now abandoned).

FIELD OF THE INVENTION

This invention relates generally to prostheses, and more particularly tofemoral components of artificial human hip prostheses.

BACKGROUND OF THE INVENTION

Load-carrying skeletal members, such as the human hip, frequently arerendered non-functional because of fracture, damage, disease, resectionsfor malignancy or disease or because of pain or malformation. Suchmembers are commonly repaired by total joint replacements withartificial components. One type of bone replacement that has beenparticularly successful over the past thirty years is that of the humanhip. Such hip prostheses typically include a femoral portion orcomponent which is implanted in the femur and an acetabular componentwhich is secured to the pelvis. The femoral component includes a headwhich rotates in a socket formed in the acetabular component. A collaris often provided on the femoral component which rests on a surface onthe proximal femur.

Many known hip prostheses require the use of cement for installation ofthe femoral component into the medullary canal of the femur. One type ofcement which is commonly used is methyl methacrylate.

Success of the femoral component of a total hip implant depends in largepart on the technical precision with which the implant is inserted.There are several factors which contribute to the success of a femoralcomponent. First, for a cemented component, the component should becentered within the central cavity in the medullary canal of the femurinto which the femoral component is inserted. Centering of the componentinsures that the thickness of the cement mantle surrounding thecomponent is uniform on all sides. Uniformity of the cement mantlerenders the load distribution at the bone-cement and metal-cementinterfaces generally uniform on all sides of the component, thusavoiding problems associated with overstressing one area of theinterface, such as fracturing of the mantle or separation of the mantlefrom the bone or separation of the component from the mantle.

Another factor which has been identified as contributing to the successof either an uncemented or a cemented femoral component is that thefemoral component should be rotated about its axis into the properangular position with respect to the femur for stability and range ofmotion. Proper rotational position, or so-called anteversion, allows foraccurate reproduction of the mechanical orientation of the hip joint.

A third factor is that the component should be prevented from rotatingonce it is seated in the femur. For cemented components, such rotationalcontrol is very important, particularly during insertion and hardeningof the cement, and any false motion while the cement is hardening hasbeen found to be detrimental to the overall results of a cementedfemoral stem. Uncontrolled rotation prior to hardening of the cementcould result in a stem which is not properly centered and which does nothave the proper angular position once the cement hardens. For uncementedcomponents, it is still important that rotational stability be achievedafter implantation of the component.

To reduce manufacturing costs and inventory requirements, it isdesirable to standardize components to the greatest extent possible, sothat one style or design can be used for most patients. Since differentsizes of components are required for patients of different stature orage, the manufacture and storage of different styles for each sizecomponent is considered highly undesirable. However, the strength,configuration and amount of available bone on the proximal femur variesgreater from patient to patient, even for patients who require the samesize components. For example, on many patients the bone mass on theproximal femur is so small or is configured such that only a smallportion of the collar on the femoral component rests on a bone surface.Thus, standardization requires that the design selected for a componentbe able to accommodate these large differences in strength,configuration and size.

Many efforts have been made in the past to design components whichresist rotation or which tend to be self centering. Examples of suchcomponents include those found in the following U.S. Pat. Nos.:5,116,380; 5,108,452; 4,946,379; 4,936,863; 4,783,192; 4,770,660;4,678,571; 4,623,353; 4,535,487; 4,068,324; 4,012,796; 2,719,522; and2,682,265. However, none of the foregoing designs is completelysuccessful in both preventing rotation of the component once implanted,and insuring that the component is held in a properly centered position.In addition, some of the foregoing designs would not operate to preventrotation or lateral movement in all femurs due to the limited lateralextent of the devices used. In some patients, the devices would notengage any bone because of its irregular configuration or lack of bonemass. Moreover, while spacers, such as those disclosed in U.S. Pat. No.5,116,380, have been used for the purpose of automatically centering thecomponent within the medullary canal, such spacers do not serve toprevent rotational movement of the prosthesis during cement hardening.Finally, spacers can interfere with the movement of the cement aroundthe edges of the component, thus, on occasion producing voids or gaps inthe cement mantle.

It is therefore an object of the present invention to provide animproved femoral component for a hip prosthesis.

It is another object of the present invention to provide a femoralcomponent which is self centering.

It is a further object of the present invention to provide a femoralcomponent which allows the physician to insert and maintain thecomponent with the proper angular position.

It is another further object of the present invention to provide afemoral component which is prevented from rotating or moving laterallyduring hardening of the cement, and which can be used with manydifferent sizes and shapes of bones.

It is yet another further object of the present invention to provide amethod and apparatus for inserting into a femur an improved femoralcomponent.

SUMMARY OF THE INVENTION

These and other objects of this invention are achieved by a femoralcomponent of a prosthetic device for the human hip, in which fins orother like protrusions are provided on the underside of the collar andin which the fins seat in corresponding, previously formed slots orgrooves in the proximal femur. These fins or protrusions, and theircorresponding mating slots or grooves in the proximal femur position thecomponent so that it is centered within the cavity formed in themedullary canal in the femur and so that the component has the properangular position or anteversion with respect to the femur. In addition,these fins and their mating grooves prevent rotation and lateralmovement of the component during hardening of cement.

In one embodiment, two elongated, non-parallel fins are provided. Thetwo fins can either intersect or they can be spaced apart to form anacute angle with respect to one another. In another embodiment, asingle, continuous fin is provided which has a curved or non-rectilinearshape. Regardless of the configuration, the fins can be retrofitted ontoexisting collars on femoral components, or they may be molded integrallywith the collar as it is being formed.

In another aspect of the present invention, a method and apparatus aredisclosed for prior formation of the slots or grooves into which thefins extend. A further aspect of the invention relates to a method andapparatus for insertion and cementing of the femoral component into thefemur.

The apparatus includes a conventional rasp which is inserted into themedullary canal. The rasp has a post on its proximal end which extendsbeyond the proximal femur. A mill guide is adapted to be snap-fittedonto the post and is prevented from rotation by a peg extending into therasp. The mill guide is provided with slots corresponding to the slotsor grooves to be formed on the proximal femur. A rounded depression isdisposed on the upper surface of the mill guide in association with eachslot. An end mill or milling bit includes an outer housing which has aball pivot adapted to reside in a corresponding depression on the millguide. The housing is adapted to be pivoted back and forth about itsball pivot as the milling bit is rotated by a conventional drill motor.The position and depth of penetration of the milling bit is carefullycontrolled by the mill guide, so that as the milling bit is pivoted,precisely formed slots or grooves are formed on the proximal femur whichcorrespond exactly in size and location to the fins disposed on theundersurface of the collar. The precise positioning of the mill guideallows for proper centering and rotational positioning of the installedfemoral component. A clamp is also provided for holding the femoralcomponent in place once it has been inserted into the medullary canal toprevent the component from moving axially out of the canal while thecement is hardening.

In the method of the present invention, a conventional rasp is used toenlarge and clean out the medullary canal of the femur in a conventionalmanner. Thereafter, the rasp is firmly and securely inserted into theenlarged medullary canal with the desired angular orientation for thefemoral component. The proximal femur is then machined in conventionalmanner to form a flat and smooth surface. Thereafter, the mill guide issnapped onto the post on the rasp, in the desired rotationalorientation. A milling bit with its associated housing is inserted intothe mill guide so that the ball pivot of the housing thereof rests in acorrespondingly formed depression in the mill guide. The milling bit ispositioned to extend a predetermined distance below the base of the millguide so that it engages the bone surface of the proximal femur. As thedrill is activated, the milling bit is pivoted back and forth along apreformed slot in the mill guide for formation of the desired groove orslot in the proximal femur. This process is repeated for each of theslots in the mill guide if more than one fin is desired. Once thisprocess has been completed, the femoral component is inserted so thatfins on the lower surface of the collar seat in the correspondinglyformed slots or grooves in the proximal femur. Thereafter the componentis clamped to the femur.

The apparatus and method of this invention centers the component in thecavity formed in the medullary canal, replicates the proper anteversion,prevents rotation of the component once seated and insures a better bondby clamping the component during hardening of the cement. This apparatusand method may be used in conjunction with either cemented or uncementedcomponents.

DESCRIPTION OF THE DRAWINGS

The invention will be more fully appreciated from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a prosthetic hip implant showing thefins of the present invention;

FIG. 2 is a cross-sectional bottom view taken along the line 2--2 ofFIG. 1 just below the collar;

FIG. 3 is a cross-sectional top view taken along the line 3--3 of FIG. 1just above the collar;

FIG. 4 is a cross-sectional side view taken along the line 4--4 of FIG.3;

FIG. 5 is a cutaway, perspective bottom view of a prosthetic hip implantshowing another embodiment of the fins of this invention;

FIG. 6 is a bottom elevational view of the implant of FIG. 5;

FIG. 7 is a cutaway, perspective bottom view of a prosthetic hip implantshowing yet another embodiment of the fins of this invention;

FIG. 8 is a bottom elevational view of the implant of FIG. 7;

FIG. 9 is a cross-sectional side view of a femur showing the rasp andthe snap-on mill guide;

FIG. 10 is a perspective view showing use of the mill guide and millingbit to form a slot in the proximal femur;

FIG. 11 is a top view of the mill guide;

FIG. 12 is a partially cutaway, cross-sectional side view of theproximal femur and mill guide illustrating use of the milling bit toform a slot in the proximal femur;

FIG. 13 is a top perspective view illustrating insertion of theprosthetic hip implant of this invention into the medullary canal of theproximal femur;

FIG. 14 is a perspective view showing the prosthetic hip implant of thisinvention being clamped into position on the proximal femur duringhardening of the cement;

FIG. 15 is a side elevational view of the clamp shown in FIG. 14;

FIG. 16 is a front elevational view of the clamp of FIG. 15;

FIG. 17 is a perspective view of a stamp employed in another embodimentof the method for forming the slots in the proximal femur;

FIG. 18 is a partially cutaway, cross-sectional side view of theproximal femur illustrating use of the stamp of FIG. 17; and

FIG. 19 is a perspective view further illustrating the use of the stampof FIG. 17.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference now to the drawings, and more particularly to FIG. 1thereof, one embodiment of this invention will be described inconjunction with a femoral component 10. It is to be understood thatcomponent 10 can be implanted either with or without cement. Component10 includes a femoral head 12 and a femoral stem 14 which is adapted tobe inserted into a cavity formed in the medullary canal of a femur 16(see FIG. 13). Stem 14 includes a large, flat laterally extending collar18 having a lower surface 19. Surface 19 of collar 18 is adapted to reston the cortical bone of the proximal femur in the region of the naturalfemoral neck. Typically, head 12 is coupled to stem 14 by a Morse conefemoral neck 20 connected to collar 18. When head 12 is inserted ontoneck 20, a very firm friction fit is formed, and no additional fastenersare required. Head 12 may be readily removed by proper twisting andpulling in the event it needs to be changed or replaced for any reasonafter implantation.

Typically, stem 14 is held in place in the medullary canal of the femurby the use of cement, such as a methyl methacrylate cement. It ispreferred that the mantle formed by the cement surrounding stem 14within the canal be of approximately the same thickness on all sides ofstem 14. Thus, stem 14 should be centered within the canal. In addition,it is highly desirable that accurate replication of the anteversionselected during insertion of the trial implants be achieved. Finally,stem 14 should not be permitted to move while the cement is hardening.

To achieve these results, fins 22 are provided on lower surface 19 ofcollar 18. Fins 22 are adapted to seat in correspondingly formed slotsor grooves 24 (FIG. 9) on surface 46 (FIG. 5) of the proximal femur. Toperform the three functions set forth above, and to provide aconfiguration that will perform these functions when used with mostfemurs, regardless of strength, shape, size and available bone surface,it is preferred that there be at least two non-parallel fins 22 formedon lower surface 19 of collar 18, or a single non-rectilinear fin havingnon-parallel portions. In one embodiment as shown in FIGS. 1-4, twoseparate, spaced fins 22 are provided. Each fin 22 has a length greaterthan its width and projects from lower surface 19 of collar 18.Preferably fins 22 extend from the outer edge 21 of collar 18 to a pointwhere they almost touch stem 14. In the embodiments of FIGS. 1-4, fins22 form an acute angle with respect to one another, but do not touch.Fins 22 converge towards one another in the direction of stem 14, anddiverge away from one another in the direction facing away from stem 14.

Other embodiments of this invention are illustrated in FIGS. 5-8. Withrespect to FIGS. 5 and 6, a single fin 30 is provided on surface 19 ofcollar 18. Fin 30 has a curved, semi-circular or semi-ellipticalconfiguration in which ends 32 face outwardly away from stem 14 and theclosed or curved portion is adjacent item 14. Fin 30 can have any shapeor radius of curvature, so long as it is non-rectilinear and so long asit extends a substantial distance across surface 21 of collar 18.

In FIGS. 7 and 8, two fins 34 and 36 are provided. Fins 34 and 36 aregenerally orthogonal to one another, and intersect one another at asingle point. Preferably, fin 34 extends from edge 21 almost to thesurface of stem 14, while fin 36 traverses almost the entire distancelaterally across the surface 19 of collar 18. Fins 34 and 36 typicallyform a plus sign or cross configuration. However, fins 34 and 36 couldbe disposed at an angle other than 90° with respect to one another, solong as they are not parallel to one another.

Fins 22, 30, 34 and 36 can be either milled from the material of collar18 and formed integrally therewith, or they can be bonded or retrofittedto surface 19 of collar 18 after collar 18 has been formed. In thelatter embodiment, fins 22, 30, 34 and 36 could be formed of methylmethacrylate cement which has been molded into the desired shape andbonded to surface 19 of collar 18.

It will be appreciated that more than two fins could be provided, orother configurations are possible, so long as the fins prevent bothrotational movement of the implanted stem 14 with respect to the femurand lateral movement of stem 14 in a direction generally normal to thedirection of elongation of the femur. Moreover, the fins must have aconfiguration which allows corresponding depressions to be readilyetched into surface 46 of the proximal femur. Also, the fins must extendsufficiently far across surface 19 of collar 18 that each fin, or eachnon-parallel portion of the same fin, engages the bone in the proximalfemur over a sufficient distance to adequately prevent rotation andlateral movement of stem 14. Preferably, the coverage of the fins onsurface 19 of collar 18 should be sufficiently great that all of theserequirements are met for patients regardless of the bone strength,configuration, mass or size so that a standard design can be used withmost patients.

The method of this invention and the apparatus used to implement thismethod will now be described with particular reference to FIGS. 9-14. Itis to be understood that this same method and apparatus can be used fora cemented or uncemented implant. The tools employed include a rasp orbroach 40, mill guide 48, end mill or milling bit 70 and clamp 92.Broach 40 is substantially similar to a conventional broach used forenlarging the medullary canal of a femur. As previously indicated,broach 40 has the same shape as stem 14, but is larger in size. Theouter surface of broach 40 is coaxial with the outer surface of stem 14,but the distance between the central axis of broach 40 and its outersurface is greater than the distance between the central axis of stem 14and its outer surface. Serrations 41 are provided along the outersurface of broach 40 for assisting in the enlarging and cleaning out ofthe medullary canal to from a cavity. Extending from an upper surface 44of broach 40 is a shaft 42. Disposed near the upper end of shaft 42 is arecess 50 into which a spring mounted ball (not shown) on an attachmentcan seat for a snap-fit. A generally circular hole 54 is formed onsurface 44 adjacent shaft 42.

Mill guide 48 is used for forming grooves or slots 24 on surface 46.Mill guide 48 includes machined slots 58 which extend from an uppersurface 62 to a lower surface 64 of mill guide 48. Mill guide 48 has thesame number of slots 58 as there are fins on collar 18. In addition,slots 58 have the same general configuration as the fins on collar 18.Disposed on upper surface 62 in association with each slot 58 is asemi-circular depression 60. Shaft 42 is intended to be inserted into achannel 52 of mill guide 48, and a spring mounted ball (not shown) inchannel 52 provides a snug snap-fit of mill guide 48 onto shaft 42.

Milling bit 70 is utilized to machine grooves 24. Milling bit 70 has arotatable shaft 74 and outer housing 72 which does not rotate and iscoaxial with shaft 74. Proximal end 76 of shaft 74 is adapted to bemounted into a chuck of a conventional drill, while distal end 78 isprovided with a milling tip which is adapted to cut bone. A shoulder 80provided adjacent proximal end 76 limits-axial movement of shaft 74 withrespect to housing 72. Generally spherical ball 82 is disposed at thelower end of housing 72 and is adapted to seat in depression 60 of millguide 48.

The uses of these tools to perform the method of the present inventionwill now be described. Initially, the femur is prepared for surgery in aconventional manner. Rasp or broach 40 is used to clean out and enlargethe medullary canal to form a cavity in the center of the femur toprepare for insertion of stem 14, so that the outer surfaces of stem 14are spaced a predetermined distance from the inner surface of the cavityformed.

In a conventional manner, the upper surface of the proximal femur ismilled smooth and flush with the upper surface 44 of broach 40 toprovide a relatively flat surface 46 on the proximal femur upon whichsurface 19 of collar 18 can rest. This process is typically accomplishedusing a large rotatable milling tool (not shown) which is mounted onshaft 42 and is rotated by a conventional drill (not shown). Oncesurface 46 has been prepared as described, mill guide 48 is snapped ontoshaft 42. Recess 50 cooperates with a spring mounted ball (not shown)within channel 52 to hold mill guide 48 snugly in place so that lowersurface 64 is in contact with surface 44. Peg 56 disposed on lowersurface 64 resides in cooperatively formed hole 54 in surface 44 toprevent mill guide 48 from rotating with respect to shaft 42.

A slot 58 is provided for each fin 22. Slots 58 of mill guide 48 areconfigured to provide a slot or groove 24 on surface 46 of the proximalfemur which corresponds almost precisely to the size and shape of theselected fins 22 or 30 or 34 and 36 to be provided on collar 18. If, forexample, fins 22 have the shape and configuration as shown in FIG. 1,slots 58 would have the shape and configuration shown in FIG. 11. If, onthe other hand, a fin 30 is to be utilized, a single slot would beprovided in mill guide 48 having the same semi-circular shape orsemi-elliptical configuration of fin 30. In this event, only a singledepression 60 would be provided on surface 62 at roughly the center ofthe slot. If fins 34 and 36 are to be utilized, two intersecting slotswould be provided in mill guide 48, and a single depression 60 would bedisposed on surface 62 at the point of intersection of the slots.

The manner of creation of these slots or grooves 24 will now bedescribed with reference to FIGS. 10 and 12. Milling bit 70 is utilizedfor this purpose. Shoulder 80 is pushed into abutment with proximal end84 of housing 72, and ball 82 is seated in cooperatively formeddepression 60. Thereafter, the drill is activated and distal end 78 ofshaft 74 penetrates surface 46 of the proximal end of femur 16 tosubstantially the same depth as fin 22 when surface 19 of collar 18rests on surface 46. Groove 24 is formed by pivoting housing 72 aboutball 82 to move shaft 74 back and forth through slot 58 while shaft 74is being rotated by a drill (not shown). In this way, the cutting ofeach groove 24 is precisely controlled and each groove 24 is formed withthe desired location, depth and width.

Using this method, groove 24 will be deepest at a point directly belowdepression 60 and shallowest at points spaced farthest from depression60 in a direction parallel to surface 46. This groove 24 will have asomewhat arcurate shape with a radius equal to the distance from thecenter of ball 82 to the tip of distal end 78. Accordingly, fins 22, 30,34 and 36 preferably have the same arcuate shape with the same radius ofcurvature. Also, fins 22, 30, 34 and 36, if viewed from the end,preferably have a U-shaped configuration to conform to the U-shapedcross-sectional configuration of recess 24 as formed by tip 78.

Once the foregoing process has been completed, and grooves 24 have beenformed, milling bit 70, mill guide 48 and broach 40 are all removed fromthe femur and stem 14 is inserted as shown in FIG. 13. Fins 22 areinserted into corresponding grooves 24, and preferably force is appliedto the upper surface of component 10 to drive it downwardly into thefemur so that fins 22 seat securely and tightly in grooves 24. Theinsertion of stem 14 is accomplished in conjunction with the provisionof cement within the cavity in the medullary canal within femur 16, in aconventional manner. Fins 22 automatically center stem 14 within themedullary canal to produce a uniform mantle, to prevent rotation ofcomponent 10 during the time the cement is curing, and to produceprecise replication of anteversion.

Another feature of this invention will now be described with particularreference to FIGS. 3, 4 and 14-16. As is shown in FIGS. 3 and 4, adepression 90 is formed in the upper surface of collar 18. A clamp 92 isused in conjunction with depression 90 to provide a downward force onstem 14 while the cement is hardening to make certain that surface 19 ofcollar 18 is urged snugly against surface 46, and that fins 22 areseated in corresponding grooves 24 so that the resulting bond is tightand so that component 10 is in precisely the desired rotational andlateral orientation.

Clamp 92 includes a stem 94 having an arcuate upper portion 96, a ball98 secured to the distal end of upper portion 96, a carriage 104, aflange 102 and a compression spring 100. Stem 94 extends through a holein carriage 104, and carriage 104 slides along stem 94. A set screw (notshown) in carriage 104 rides in an axially extending slot along stem 94(not shown) to limit axial travel of carriage 104, and to preventrotational movement of carriage 104 with respect to stem 94. Carriage104 includes one or more spikes 106, which extend from one side thereoftoward ball 98, and finger grips 105. Spring 100 is captured betweencarriage 104 and flange 102 and urges carriage 104 in a direction awayfrom flange 102.

Use of clamp 92 will now be described with particular reference to FIG.14. Ball 98 is seated or nested in depression 90 in collar 18. With athumb pressing against flange 102, and two fingers pressing downwardlyon finger grips 105, carriage 104 is withdrawn downwardly towards flange102. At the same time spikes 106 are driven into engagement with thelesser trochantor. As the downward pressure on carriage 104 is released,spikes 106 dig into the lessor trochantor, and spring 100 biases stem 94so that ball 98 is urged toward carriage 104. Spring 100 thereby appliesa downward pressure to ball 98 which then urges component 10 downwardlyto properly seat stem 14 within femur 16. Clamp 92 is removed once thecement has properly hardened. Removal is accomplished by compressingspring 100 between carriage 104 and flange 102 and withdrawing spikes106 from the lessor trochantor.

Clamp 92 applies the requisite seating force to component 10 with littledamage to the bone or surrounding tissues. Clamp 92 is easily operatedand readily removed by the physician.

Another embodiment of this invention will now be described withreference to FIGS. 17-19. This embodiment can be used either with orwithout cement. Like numbers are used for like parts, where applicable.In this embodiment, fins again are disposed on surface 19 of collar 18of component 10. These fins may have any one of the shapes previouslydescribed, particularly with respect to FIGS. 2-8. In this embodiment,as in the previous embodiments, corresponding grooves are cut intosurface 46 of the proximal femur for accepting the fins, prior toimplantation of the component. This embodiment differs from that ofFIGS. 9-12 in the manner of formation of the grooves for accepting thefins.

In this embodiment, instead of mill guide 48, a stamp 120 is mountedonto shaft 42 of broach 40. Stamp 120 includes a peg 122 which extendsinto hole 54 for proper orientation of stamp 120 and for preventingrotation of stamp 120 during the cutting process. Projections 126 onlower surface 124 of stamp 120 have sharpened edges along the surfacethereof confronting surface 46 of the proximal femur. Projections 126have precisely the same shape, orientation and size as fins 22, 30 or 34and 36 disposed on surface 19 of collar 18. Once stamp 120 has beenmounted onto shaft 42, stamp 120 is driven downwardly against surface 46by a hammer 132, or other like tool for applying force, to driveprojections 126 into surface 46 of the proximal femur. This operationstamps into surface 46 grooves which have exactly the same size, shapeand orientation as selected fins 22, 30 or 34 and 36. Once surface 124has been driven into firm and uniform contact with surface 44, stamp 120and broach 40 are removed. Component 10 is thereafter inserted aspreviously described, so that the fins seat in the grooves formed insurface 46 of the proximal femur. Thereafter, the implantation processis completed, precisely as described previously with respect to theembodiments of FIGS. 9-12.

Typically, shaft 42, mill guide 48, shaft 74 of milling bit 70, clamp 92and plate 120 are all formed of a hard, corrosion resistant materialsuch as stainless steel. However, other known, hard materials may beused. For purposes of illustration only, typical dimensions of the finsof this invention will be provided. However, it is to be understood,that by providing such examples, the scope of the invention is in no waylimited. In a typical implant, fins 22 would each have a length of about1 cm and a width of about 1 mm. Fin 30 would have an approximate radiusof curvature of 1 cm and a total length between ends 32 of about 15 mm.Fins 34 and 36 would typically each have a length of about 1 cm. Thesizes and shapes of the tools used for implantation, as describedherein, would be selected in accordance with the sizes and shapes of theparticular femur upon which the surgical operation is being performed.

The foregoing invention provides a method and apparatus for centering astem within the cavity in the medullary canal of the femur, permittingaccurate reproduction of anteversion, preventing rotation once theprosthetic has been seated, and clamping the prosthetic during seatingto insure a good cement bond. As a result, a uniform mantle of cement isprovided around the circumference of the stem which optimizes loaddistribution between the bone-cement and metal-cement interfaces, thusrendering less likely failure due to nonevenly distributed stresses.Accurate reproduction of anteversion improves the quality of the implantand improves relative movement within the joint so that the patient canenjoy more nearly normal and pain-free activity. Rotational controlprevents false movement while the cement is hardening insuring properrotational orientation and improving the chances of a better cement bondand longer life for the prosthetic. Clamping during seating also insuresa better and tightly cemented bond. The method and apparatus of thisinvention also have applicability to uncemented components since theypermit accurate reproduction of anteversion and prevent rotationalmovement of the prosthetic once it has been implanted.

In view of the above description, it is likely that modifications andimprovements will occur to those skilled in the art which are within thescope of this invention. The above description is intended to beexemplary only, the scope of the invention being defined by thefollowing claims and their equivalents.

What is claimed is:
 1. Apparatus for cutting grooves in a surface on aproximal end of a bone adjacent an opening of a cavity formed in thebone into which a prosthetic device is to be inserted, said apparatuscomprising:a mount adapted to seat securely in the cavity of the bone; aguide having a lower surface and an upper surface and being mounted onsaid mount, said guide having at least one slot extending from saidupper surface thereof to said lower surface and being adapted to overliethe surface on the proximal end of the bone, said guide having a curveddepression disposed on said upper surface contiguous with said slot;apparatus disposed on said guide and said mount including a shaft and acorrespondingly formed channel for slidably receiving said shaft formounting said guide onto said mount; and a milling tool, said millingtool having a curved surface disposed thereon and a distal end, saidcurved surface corresponding in shape with said depression and beingadapted to seat in said depression on said upper surface of said guideto limit penetration of said milling tool into the surface on theproximal end of the bone, said guide being configured to facilitatepivoting of said milling tool about said depression during activation ofsaid milling tool to cause said distal end of said milling tool to movewithin said slot in said guide in a direction generally parallel to saidlower surface of said guide to form a groove in the surface on theproximal end of the bone.
 2. The apparatus of claim 1 wherein said guidecomprises a second slot, said second slot being oriented in a directionwhich is not parallel to said first slot.
 3. The apparatus of claim 1further comprising a peg for preventing rotation and lateral movement ofsaid guide with respect to said mount.
 4. The apparatus of claim 1wherein said slot in said guide comprises two opposed, substantiallysmooth sidewalls extending from said upper surface to said lower surfaceof said guide.
 5. Apparatus for cutting grooves in a surface on aproximal end of a bone adjacent an opening of a cavity formed in thebone into which a prosthetic device is to be inserted, said apparatuscomprising:a guide adapted to be mounted adjacent to the surface on theproximal end of the bone, said guide having a lower surface and an uppersurface, said guide having at least one slot extending from said uppersurface thereof to said lower surface and being adapted to overlie thesurface on the proximal end of the bone, said guide having a curveddepression disposed on said upper surface contiguous with said slot; anda milling tool, said milling tool having a curved surface disposedthereon and a distal end, said curved surface corresponding in shapewith said depression and being adapted to seat in said depression onsaid upper surface of said guide to limit penetration of said millingtool into the surface on the proximal end of the bone, said guide beingconfigured to facilitate pivoting of said milling tool about saiddepression during activation of said milling tool to cause said distalend of said milling tool to move within said slot in said guide in adirection generally parallel to said lower surface of said guide to forma groove in the surface on the proximal end of the bone.
 6. Theapparatus of claim 5 further comprising:a mount adapted to seat securelyin the cavity of the bone; and tool securing means for mounting saidguide on said mount, said tool securing means having a channel adaptedto slidably receive a shaft, said guide being slidably removable fromsaid mount by application of force to said guide directed away from saidmount.
 7. The apparatus of claim 5 wherein said slot in said guidecomprises two opposed, substantially smooth sidewalls extending fromsaid upper surface to said lower surface of said guide.